1. Field of the Invention
The present invention relates generally to noise detection and more particularly to systems and methods of compensating for noise.
2. Description of Related Art
Conventional noise detectors and audio noise compensation systems suffer from a variety of limitations. A primary limitation is a slow, inaccurate and/or costly noise detector. FIG. 1 shows a conventional noise detector in which microphone 100 detects the acoustic noise signal which is amplified and provided to power estimator 120 to produce an environmental noise level 130. Power estimator 120 typically consists of a rectifier and lowpass filter. When used in an application such as a phone, the caller's speech dominates the microphone signal resulting in an erroneous higher noise level indication.
For systems that increase system output volume in response to noise, the effect of the caller's speech results in the output level increasing every time the caller speaks then decreasing when the caller ceases speaking. To reduce this undesirable behavior, the attack time of power estimator 120 is reduced in an attempt to avoid responding to the caller's speech. However, this results in unacceptably slow response times and it may well be faster to manually adjust the volume level.
To increase the response time, multiple microphones have been used, one to detect mainly the caller's voice and a second to detect mainly the background noise level. The microphones need to be matched and as the microphones age, they become mismatched resulting in degraded operation. There is also an additional cost for matched microphones. An alternative is to perform a “matching operation” every time the device is operated. Another alternative is to have a “bone conduction microphone” detect the caller's voice for removal from the main microphone signal. This requires the bone conduction microphone to be in contact with the caller's skin, which can be uncomfortable for long durations. The contact quality is also affected by the caller's mouth movements which alters the amount of skin contact pressure.